The use of steam in tunnel finishers has proven to be effective in de-wrinkling the fabrics of garments and other textile products. The properties of water vapor in the form of steam are excellent for imparting a rise in temperature in the fabric by penetrating the weave and layers of fabric. The moisture content of a fabric aids in the transfer of heat from the air stream to the fabric weave, and also is known to soften cotton fibers. Increasing the temperature of fabric under the presence of moisture in the fabric combined with moisture in the air in the form of steam is essential to the complete de-wrinkling process. Steam is nearly always used for direct injection to the fabric. Steam also may be used for convective air heating and re-heating systems and to re-heat into steam vapor the excess condensate resulting from direct injection steam systems.
Typically, tunnel finishers use pressurized steam from boilers in the pressure range of 40-125 psig (2.8-8.6 bar) with some operating as high as 175 psig (12 bar). The pressurized systems deliver the latent heat of steam plus additional sensible heat due to the higher pressures. This provides ample amounts of heat energy to the textiles. Also, pressurized steam aids in delivering the steam with physical force into the fabric weave thereby achieving penetration of the moisture and heat into the fabric.
While use of high pressure steam is effective in large commercial garment finishing operations where operating a pressurized boiler and steam system is convenient and cost effective, other commercial garment operations have difficulties justifying the high cost, space, technical and regulatory requirements of such pressurized steam systems. In cases in which other laundering processes are not performed on the same site, the only reason to use pressurized steam can be the tunnel finisher itself. Tunnel finishers use live steam, or steam under pressure, for direct injection to the fabric, thus a high degree of steam loss to the surrounding atmosphere is incurred. This loss requires a higher than usual percentage of added feed water to be used in generating the live steam, rather than relying on return condensate which is more economical to re-convert into steam. As a result of this steam loss and the use of live steam a comparatively large boiler system is required for the selected size and scope of the tunnel finisher employed.
A further drawback is that pressurized boilers are subject to certain regulatory requirements that vary widely from country to country, state or province to state or province, county to county, and city to city. This represents an added barrier to the efficient manufacture of tunnel finishers and to their installation. Some jurisdictions regulate boiler operations by placing a limit on the boiler size as measured in boiler horse power (Bhp) before more stringent safety and operational precautions are required by the jurisdiction. For example, for some jurisdictions a boiler of 10 Bhp (approx. 98 kW) or less may not be subject to boiler location and housing safety requirements of the jurisdiction. Other jurisdictions may regulate boiler operations by limiting the boiler to certain delivered steam pressures, for example, a 15 psig (1 bar) on the pressure of the steam generated by the boiler. Additional boiler regulation requirements may be in the form of a requirement for a full time, certified boiler engineer on the premises (a “stationary engineer”) or the construction of a specially enclosed room or building to house the boiler. These variations in the regulation of high pressure boilers create a difficult maize a manufacturer and/or user of high pressure steam tunnel finishers to traverse. Also, the regulations on use of high pressure boilers present a substantial added cost and complication to the operation of smaller commercial laundry and garment finishing concerns.
Typical tunnel finisher systems are designed to use piping and steam spray holes, slits, or nozzles which function well at pressures over 40 psig (2.8 bar). These systems have only marginal effectiveness at steam pressures of 15-40 psig (1-2.8 bar), and minimal or poor effectiveness at steam pressures below 15 psig (1 bar). Moreover, the potential energy available for convective air heating (heat exchangers) and reheating condensate into steam becomes less than effective below 15 psig (1 bar). At low steam pressures, conventional tunnel finisher devices cannot, in a reasonable amount of time, deliver enough heat energy to the fabric for de-wrinkling and/or moisture removal for good performance. Even for very small tunnel finishers, typical steam requirements total at least 10 Bhp (approx. 98 kW), and still suffer from the previously mentioned high make-up water requirements.
Due to onerous regulatory requirements and the high cost and complexity of pressurized boiler systems over 10 Bhp (approx. 98 kW) in size, use of a tunnel finisher becomes a difficult process to implement for those businesses and operations that do not otherwise have access to a boiler. Presently, if low-pressure steam systems are employed, the performance of the tunnel finisher will suffer, and the excess condensate tends to drain along the floor of the finisher, creating a hygiene and corrosion problem. If low pressure boilers are employed in conventional tunnel finishing devices, the boiler may not be able to heat the necessary make-up water rapidly enough, causing “boiler carry over.” “Boiler carry over” is a situation in which liquid water and water treatment chemicals are pushed through the piping systems into the injection tubes of the tunnel finisher, creating unsightly “brown spots” on the fabric and walls of the finisher, as well as excess water in the system.
Previous attempts to solve these issues were limited in effectiveness. The “Hydro Finisher” developed by Colmac Industries, Inc., in 1988 attempted to boil water directly in a chamber of the tunnel finisher by spraying water directly on a heat source. The desired finishing effect was excellent, however the machine was not able to sufficiently control the excess water and distillates to avoid self-corrosion. The “Hydro Tech” developed by Colmac Industries, Inc., in 1997 attempted to mix water into heated air to deliver super heated air/water vapor to the fabric. In this device the distillates were an issue and the effectiveness of flashing the water droplets to steam with heated air was impractical due to the high energy requirements.
Other prior art systems have attempted to use low pressure steam delivered through small, typically copper or stainless steel, tubes of less than ¾″ (19 mm) diameter to deliver steam to the fabric of the textiles being finished. These devices relied on the motive force of the pressure of the steam to deliver the steam into the fabric weave. However, as steam pressure decreased, the steam failed to sufficiently penetrate the fabric weave, and performance of these devices suffered. Other prior art systems have tried to mix water directly in the heating mixing chambers. But the amount of energy diluted from the air heating system to overcome the latent heat of evaporation to convert the water to steam reduced the air heating to ineffective levels.
Therefore, it would be a benefit if a low pressure tunnel finisher were developed which could avoid the regulatory requirements of high pressure steam boilers while providing effective and efficient low pressure steam generation that avoided “boiler carry over” and excess condensation within the tunnel finisher device.